IDENTIFICATION OF THE PROTEIN 4.1 BINDING INTERFACE ON GLYCOPHORIN-C AND GLYCOPHORIN-P55, A HOMOLOG OF THE DROSOPHILA DISKS-LARGE TUMOR-SUPPRESSOR PROTEIN

Protein 4.1 is the prototype of a family of proteins that include ezri n, talin, brain tumor suppressor merlin, and tyrosine phosphatases, Al l members of the protein 4.1 superfamily share a highly conserved N-te rminal 30-kDa domain whose biological function is poorly understood. I t is believed that the attachment of the cytoskeleton to the membrane may be mediated via this 30-kDa domain, a function that requires forma tion of multiprotein complexes at the plasma membrane, In this investi gation, synthetically tagged peptides and bacterially expressed protei ns were used to map the protein 4.1 binding site on human erythroid gl ycophorin C, a transmembrane glycoprotein, and on human erythroid p55, a palmitoylated peripheral membrane phosphoprotein. The results show that the 30-kDa domain of protein 4.1 binds to a 12-amino acid segment within the cytoplasmic domain of glycophorin C and to a positively ch arged, 39-amino acid motif in p55, Sequences similar to this charged m otif are conserved in other members of the p55 superfamily, including the Drosophila discs-large tumor suppressor protein, Our data provide new insights into how protein 4.1, glycophorin C, p55, and their non-e rythroid homologues, interact with the cytoskeleton to exert their phy siological effects.